How to Tie Rebar by lfsmj2010

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									How to Tie Rebar
Tying rebar.Building withconcreteinvolves many steps to achieve the best
results, including forming, grading, placing, andfinishing. One critical
step is placing the reinforcing bars, orrebarcorrectly, and this article
will explain how this is done.
<Steps
1Plan the project. For structural concrete construction, an engineer
andarchitectwill usually do the technical design work and provide
specific information regarding the sizes, configuration, and placement of
rebar in the associated concrete work. Planning the actual fabrication
and placement, as well as the schedule of the work is your first task.<
2Purchase the rebar.For simple projects like typical building foundations
and slab reinforcement, you can most likely buy the necessary rebar from
a building supply center or home improvement warehouse. For complicated
applications such as gradebeams, foundation walls, tanks, and other
projects, you will need to have specific shapes formed by a rebar
fabrication specialist. Here are some examples:Stirrups. These are shaped
rebar that hold the lateral reinforcement in a certain configuration,
often called acage. They create a framework that keeps these larger bars
in position, and may be round, square, rectangular, or even complex
combinations of shapes.
Dowels. These are usuallyLshapes, or straight lengths of rebar with a
ninety degree bend on one end.
Corner bars. These are alsoLshapes, with each side of theellthe same
length.
Offset bends. These range from a simpleZshape to complex angles, used in
reinforcing concrete walkway steps and steps (changes in elevation) in
concrete footings.
Hairpins. These areUshaped rebar that are often used to interlock two or
more individualmatsof rebar to give lateral strength to the concrete
casting.
Candycanes. As the name implies, these are straight lengths of rebar with
aUshaped bend on one or both ends, again to interlock two or more
parallel reinforcing mats.

3Consult your reinforcingplacement drawings/plan. If you purchase your
rebar from a fabricator, the supplier will usually review your structural
engineer's or architect's plans and produce ashop drawingwith details and
identifying tags for each type of rebar used in the project. For simpler
projects, your building plans should provide spacing requirements and bar
sizes. Use these documents to determine where and what rebar is needed in
individual locations.
4Choose the method you will use totiethe rebar.Most times, rebar is tied
with annealed steel wire, either bought in four pound bulk rolls, or if
using abag tiespinner, in bundles of precut wire pieces with loops formed
on both ends. The latter are easier for novices to use, but somewhat more
expensive, the former is often the choice of experience rebar tyers
(rodbusters).
5Prepare the area where the concrete is to be placed.The ground should be
graded and compacted after any needed subgrading,excavations, and
underground rough ins for plumbing and electrical utilities is finished.
Lay out the actual perimeter or form lines for the concrete placement
after the grading and compaction and associated testing is done.
6Decide whether the concrete forms will be installed prior to placing
your rebar.For large footings where heavy rebar is to be used, the
formwork usually is done first, for concrete walls and grade beams, one
side of the form may be built prior to tying the rebar, but the rebar
will need to be tied in place before the formwork is completed so bars
can be positioned and tied in place. For concrete slabs, the subgrade
(ground underneath the slab) is often pre-treated for termites, and a
moisture barrier or dampproofing is installed before the mat is tied.
7Shake outthe rebar. This involves removing individual bars, stirrups,
and dowels from their respective bundles according to the placement
drawing counts. An example would be a slab measuring 12 feet by 12 feet
with rebars at 8 inch centers in one direction, and 12 inch centers the
other. Determine the size of bars required in each direction, mark two or
three bars with the appropriate layout measurements in each direction,
and count the marks to determine how many rebar are required for each
direction. Often, the placement drawings are specific, such as "18
(number 5) rebar, 11 foot 6 inches long, one half each way". This gives
the following information: You need the given quantity, 18, rebar,
size5(5/8 inch diameter), with 9 bars laying in each direction, the top
rows perpendicular to the bottom ones.
8Tie your rebar.This is the primary focus of this article. Tying the bars
so that they remain in their correct respective positions is critical to
achieve the desired strength of the completed concrete structure.
9Place each rebar in its respective positionaccording to the layout
described in the previous steps. Thelayout bars( or mark bars) can be
marked with a soapstone marker, a paint pen, a piece of lumber crayon, or
with spray paint.
10Select the appropriate type of tie you will use.For thebag ties(Snap
Ties, not to be confused with the snap ties described later). For
ordinary slab mats, where the force of the concrete interacting with the
rebar during its placement is minimal, and movement of the mats is
unlikely, using a simple, single twist of wire around each rebar
intersection, twisted together tightly, will suffice. This tie is known
as asnap tie, and can be made with the Snap Tie precut ties and aspinner,
noted earlier. It can also be done easily with a pair of 9 inch lineman's
pliers and bulk wire held on the rodbuster's workbelt in awire reel. For
other applications where the force of the concrete placement may displace
the rebars, or where more strength is needed to hold bars in the proper
configuration, more complicated ties may be used. Here are some of them,
with a simplified description of how they are made:Figure 8 ties. These
are made by pulling the wire around the rear (from the rodbuster) bar,
diagonally across the front bar, back around the rear bar, diagonally in
the opposite direction across the front bar, and then twisting back
around the beginning wire. You then cut the wire feeding off the reel,
and bend the cut ends back towards the tie so no sharp ends project from
the tie. These ties will help hold perpendicular bars tightly together
while helping to prevent them fromracking, or moving diagonally.
Saddle ties. Similar to the figure 8 tie, you begin by passing the wire
feeding from your reel behind the rear bar, then across the front bar
staying parallel to the bar. You then pass it behind the rear bar again,
back around the front bar on the opposite side. You now twist the ends
together, cut the feed wire, and bend the cut ends back. This tie is
often used when tying rebar for walls or other vertical application where
the rodbuster will actually climb on the rebar framework to access higher
portions of the wall. The figure 8 and saddle tie can often be
interchanged, however, technically speaking, there are advantages to each
one in certain circumstances.
Combinations of figure 8 and saddle ties with additionalwrapsaround
vertical rebars can be used to increase the hold of the tie so bars
cannot slip downward when weight is applied to them or the plastic
concrete is dropped into the form.

11Use your pliers for tying these ties efficiently.For all the above
mentioned ties, you pull the feeding end from the wire reel with your
non-dominant (hereafter regarded as left, please reverse for right handed
persons) hand. Grip the end of the wire with your pliers in your right
hand, andpoke, or push it behind the rebar described in the first step of
your chosen tie. Bend or angle the end toward the place you will be
grabbing the end in the next step of the tie, then reach from that side,
grip it again with the pliers, pull it toward the next place you will
route it to, pulling enough slack wire to complete the tie. Hold
resistance on the wire with your left hand, so the wire bends snugly
against the bar you are wrapping in each stage of the tie. Release the
wire so that the pliers can be used to grip it, and do so, pulling the
end around the bar and twist the two ends of the wire together. Pull or
tug the wire with the pliers so the tie is tight.
12Tie all the bars required in their correct positions.Check your plans
to make sure each component of the reinforcement is in place. Often, in
structural concrete reinforcement, you will find several elements that
interface together in addition to the basic rebar mat discussed so far.
Here are a few to note:Block dowels. When placing a concrete foundation
which will have concrete masonry units (block) erected on it, you will
usually find the plans require installing block dowels, or vertical rebar
to reinforce cells at a required spacing to give the subsequent block
wall sufficient strength to withstand conditions to which it will be
exposed, or to help it support loads it will carry as an overall part of
the structure you are building. These bars are tied to the foundation
rebar (footing bars) in a location that will place them in the center of
individual block cells. For them to be placed correctly, you will need to
establish thewall line, then determine the spacing of these cells. If
your layout begins at a corner, using 8X16 inch regular block, you can
place the first dowel 4 inches inside the outside wall line, 4 inches
from the corner, then space additional bars at their required distances
in multiples of 8 inches. For example, at 16, 24, or 32 inch centers.
This is known asblockworkspacing.
Bulkhead dowels. In instances where a footing will not be completed in a
single concrete placement, you will need todowelout of the bulkhead form
so the next placement will be structurally tied to the latter one. Make
sure the dowels extend far enough that the lateral reinforcement will
overlap enough to maintain the strength of the rods used. Typically,
rebarlapis calculated inbar diameters. An example would be the number 5
rebar mentioned earlier. It has a diameter of 5/8 of an inch, and the
required lap might be 40 bar diameters. Mulitplying the diameter 5/8 by
40, you will get 200/8, or 25 inches.
Note that in structural concrete, other types of imbeds and inserts may
be required. Place rebar in such a manner as to allow installation of
anchor bolts, sleeves, embedded weld plates, inserts, or other items in
their repective correct locations without interference. In general terms,
these items require more precise positioning, so offsetting one or two
rebars may be required.

13Chair or support your rebar.Once the mat or cage is assembled, you must
hold it in position so the the concrete will cover it completely.Rebar
chairsorconcrete brickare often used for this purpose. Place these
positioners at a spacing that will not allow the rebar to bend or deflect
enough to reduce the coverage you wish to obtain with the concrete you
place in you forms. For a 12 inch thick footing, the rebar mat is usually
placed about 4 inches from the bottom of the concrete, and side
clearances range from 2 to 4 inches.
14Observe the rebar configuration while the concrete is placed.If
shifting occurs, support the rebars with a handled tool like a shovel
wedged so that you can achieve sufficient leverage to hold its position,
or alter the direction of flowing concrete so force is applied in the
opposite direction.
15Cap or otherwise protect any exposed bars while working near them.Rebar
that issheared, or mechanically cut has very sharp surfaces at the
location of these cuts. Construction workers have suffered serious
injuries and have also been killed when they have fallen on projecting
rebar dowels. Specialrod capsmade of high impact plastic with a metal
plate embedded in them are required by the Occupational Safety and Health
Administration (OSHA), in the United States.<


Tips
Keep rebar stored on dunnage to prevent rusting, and to keep bars from
becoming buried in soft soils. Any build up of iron oxide (rust) will
exacerbate spalling later on.
Buy quality tools if you plan to do a lot of rebar tying. Cheap wire
reels and pliers won't hold up to the wear and tear of daily use.
Double check the rebar placement drawings, especially for dowels, since
misplaced dowels must be cut off, and new ones epoxied in the correct
location, at considerable expense.

<Warnings
Wear the correct safety equipment for this work. Gloves are especially
important to protect the rodbuster's hands.
Rebar ends and the ends of cut tie wire can be incredibly sharp.
Impalement protection caps are required by law in the United States.

Things You'll Need
Rebar and a rebar placement plan.
Pliers or a Snap Tie spinner.
Wire and a wire reel.
Marking crayons, soapstone, or paint.
Tape measure.

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